1. Field of the Invention
The present invention relates generally to communication systems and, more particularly, to systems and methods for signal encoding and decoding.
2. Related Art
A typical communication system employs signal encoding and decoding to achieve many significant advantages such as efficient data transmission, error correction, combating channel interference, or ensuring communication secrecy. One example of an encoder is an 8 bit to 10 bit encoder (also referred to as an 8B/10B encoder) that encodes the incoming data with certain characteristics such as run length, transition density, and direct current (DC) balance. Run length refers to the number of identical contiguous symbols permitted at the encoder output. Transition density refers to the number of symbol changes (i.e., transitions from one symbol to the other symbol) for a given number of symbols, with a minimum number generally necessary for receiver synchronization. DC balance refers to providing an approximately equal number of binary ones and zeros, which for example, correspond to respective positive and negative values to allow for alternating current (AC) coupling. The characteristics above are related as, for example, a large number of contiguous binary ones would produce a large positive DC signal and run length, but no transitions.
It is generally desirable to have codes that are efficient (i.e., a large ratio of information digits per word to word length). Conventional encoders, such as the 8B/10B encoder, do generally eliminate disparity, which is the difference between the number of binary ones and zeros in a given block of data, or the DC component of the signal and also provide sufficient transition density. One drawback, however, is that these encoders are not very efficient. For example, the 8B/10B encoder operates at the byte level by taking 8 bits to provide an encoded output of 10 bits. Consequently, the 8B/10B encoder adds two additional bits for every eight bits resulting in an overhead of twenty percent. This inefficiency or additional overhead results in associated delays and costs such as increased transmission times, storage space, and overall channel capacity and bandwidth.
As a result, there is a need for a more efficient signal encoder and decoder while still providing desirable characteristics such as low disparity and sufficient transition density.